I'm just buttoning up from a blasted spark plug and corroded, leaking intake manifold, and I have a mystery port on the driver's side fuel rail. It points straight up, and looks like it should have a small hose or electrical sensor attached, but I don't seem to have anything left over that would go there. 5.4 liter Triton V-8, 2001 F250 Super duty. TB angles towards the L headlight, mystery port sits between injectors for cylinders 6 and 7. If yours has this, which direction does the hose/wire go, and to what might it be attached?

 

My long distance mechanic/guru suggests that it could be the fuel pressure regulator, and requires a constant vacuum source. I don't see any spare vacuum hoses or an unused vacuum port on the intake manifold or the Throttle body. Any help? No help?